60 Recent Literature. [January 
to practically the same locality year after year to breed. In the efforts of 
the Fish Commission to restock our exhausted rivers with fish it has been 
found that such migratory species as the shad, when placed as fry in 
rivers remote from the habitat of their parents, return the next year not 
to the home of their ancestors, as ‘inherited habit’ would seem to de- 
mand, but to the very rivers where they were turned out as fry. Such 
phenomena seem to introduce a new problem into the question which may 
well receive serious consideration. 
Migration, as is well known, is by gradual stages, occupying many 
weeks, and often several months, and is largely influenced by meteorelogic 
conditions, which govern the ever varying rate of progress, periodically 
accelerating or holding in check the onward movement, and giving rise to 
what are known as waves of migration. The beginning of return migra- 
tion in spring is coincident with the first ‘warm wave,’ which may occur 
earlier or later according to the season. ‘This first advance is usually 
soon checked by a falling temperature, and the movement remains station- 
ary during its continuance, the retardation being governed by the length 
and intensity of the period of cold. With an immediately succeeding 
warm wave the northward journey is resumed, to again soon receive a 
more or less decided check by an alternating cold wave; and so on, with a 
greater or less number of repeated checks and impulses, till the various 
species of migratory birds have reached their summerhomes. While all 
this has long been known in a vague way, Professor Cooke has now given 
us the history of the spring migration during the years 1884 and 1885 
for alarge number of birds inhabiting or passing through the broad region 
of the Mississippi Valley, and has traced in detail many ‘bird waves,’ with 
their concomitant meteorologic conditions. It is thus demonstrated that 
in general the migratory movements of birds in spring are governed by 
atmospheric changes, notably the alternation of warm and cold waves, the 
former favoring and the latter retarding or wholly checking movement, 
according to their severity. As these alternating cold and warm atmos- 
pheric waves depend upon atmospheric pressure,— the direction of winds 
being toward an area of low barometer,— and pass across the country from 
the west toward the east, warm winds blow from the south over the region 
south of a ‘storm centre’ or area of low barometer. Thus the waves of 
bird migration during the spring movement are not only necessarily from 
the south northward, but are coincident with a warm atmospheric wave 
and a southerly wind; and the wave of migration varies in magnitude 
with the duration of the warm atmospheric wave and its intensity as 
regards temperature. 
While these are the favorable conditions for bird migration, birds move 
more or less under the ordinary conditions of the weather proper to the 
season, and are only held incheck by the unfavorable conditions of a cold 
wave, accompanied by northerly winds and a sometimes fatal reduction 
of temperature. 
Professor Cooke gives the average rate of movement of certain birds 
based on the data collected, from which it appears that the Baltimore Oriole 
